There are numerous circuits and other electronic devices that produce energy waves, such as electromagnetic waves and microwaves. These circuits produce energy waves that are delivered to a destination through different wires, guides, and other mediums.
Transitioning microwave signals from one mode to another or interfacing to another medium is “lossy.” By being lossy, a portion of the signal is lost as it travels through the circuits, wires, and other mediums. Stated another way, a signal entering a lossy material will be greater at the point of entry than at the point of exit.
Transitions at microwave frequencies are particularly difficult and lossy. Dielectric materials have higher loss tangents at microwave frequencies versus lower frequencies. At microwave frequencies metal losses become greater due to reduced skin depth and increased sensitivity to surface roughness. Apart from materials being lossier at microwave frequencies, the design of the transitions and interfaces is more difficult. It is difficult to control or predict phase at microwave frequencies. This leads to greater mismatch losses. Typically, the simpler an interface is, the less loss it will experience. One exemplary circuit that generates and transports microwaves is a “monolithic microwave integrated circuit” or “MMIC.” Lost signal waves are unusable and decrease the efficiency of a MMIC as the signal strength decreases due to loss. Generally, the higher the frequency of the microwave, the more lossy the transmission medium and more inefficient the circuit. In certain applications, even signal losses that reduce the signal small amounts, such as 1/10 of a decibel, may result in a significant performance loss. One exemplary application where loss from energy waves such as microwaves is problematic is a power amplifier.
One structure used to reduce lossiness is a waveguide. Waveguides are structures that define a cavity that carries energy waves to a particular destination. Unfortunately, signal loss is still problematic with certain waves because the connection or interface between the circuit generating the energy waves and the waveguide can be lossy itself.
The interfaces between a waveguide and an integrated circuit tend to be lossy in part, due to the initial transition from a circuit such as a MMIC to the interface. This initial transition between an integrated circuit and an interface is lossy due to the impedance difference between the integrated circuit and interface. One way to reduce this initial loss is to closely match the impedance of the MMIC or other integrated circuit with the interface at the transition point.
MMICs have some of the greatest and most noticeable amounts of signal loss due to due to the types of interfaces used to connect MMICs to other energy transmission devices, such as waveguides. Moreover, impedance miss-matches from the MMIC to the waveguide enhance signal losses. For example, the impedance of the MMIC, for example fifty ohms, may not match the impedance of the connected waveguide, which is much higher, typically several hundred ohms higher than the impendence of the MMIC. Further, the MMIC and waveguide also likely have different modes of energy wave propagation.
Current interfaces between a MMIC and waveguide comprise numerous structures that include wirebond, microstrips, pins, and other devices to connect a circuit to a waveguide or another structure. Each part of a matching network has associated loss. These interfaces also attempt to match and transform the impedance of the MMIC to the impedance at the waveguide. These types of interfaces are known generally as “impedance matching interfaces” or “impedance matching and transforming interfaces” and these interfaces transform impedance and wave mode propagation of the energy traveling through the interface. Throughout, the term “interface” is meant to denote an “impedance matching interface” or “impedance matching and transforming interface.” However, current impendence matching interfaces between an integrated circuit such as a MMIC and a waveguide still have an unacceptable amount of loss. Much of this loss is due to the extra components such as microstrips, suspended strip lines and pins that result in higher loss.
Besides lossiness, MMICs and other similar circuits suffer from an excess of “ripple.” Ripple is unwanted gain variation versus frequence due to the mismatch of impedances at two electronic devices, such as a microstrip track and MMIC or from a microstrip to a suspended stripline or from a suspended stripline to a waveguide. When there is a mismatch, there is a return wave that generates a standing wave. This standing wave is what causes the ripple versus frequency.
Therefore, it would be advantageous to provide an interface between an integrated circuit, such as a MMIC, and a waveguide, or other structure that reduces signal loss. It would also be desirable to produce an interface that reduced ripple to decrease loss. It would also be desirable if the interface was configured to closely match the impedance of the MMIC to the interface at the transition point. It would further be advantageous to produce an interface that reduced loss that was inexpensive and easy to manufacture, particularly one that was constructed from parts that were commercially available and did not require the use of dielectric materials or microstrips and one that directly wirebonded an integrated circuit such as a MMIC to a waveguide.